The invention relates to compressors. More particularly, the invention relates to compressors having check valves.
Screw-type compressors are commonly used in air conditioning and refrigeration applications. In such a compressor, intermeshed male and female lobed rotors or screws are rotated about their axes to pump the working fluid (refrigerant) from a low pressure inlet end to a high pressure outlet end. During rotation, sequential lobes of the male rotor serve as pistons driving refrigerant downstream and compressing it within the space between an adjacent pair of female rotor lobes and the housing. Likewise sequential lobes of the female rotor produce compression of refrigerant within a space between an adjacent pair of male rotor lobes and the housing. The interlobe spaces of the male and female rotors in which compression occurs form compression pockets (alternatively described as male and female portions of a common compression pocket joined at a mesh zone). In one implementation, the male rotor is coaxial with an electric driving motor and is supported by bearings on inlet and outlet sides of its lobed working portion. There may be multiple female rotors engaged to a given male rotor.
When one of the interlobe spaces is exposed to an inlet port, the refrigerant enters the space essentially at suction pressure. As the rotors continue to rotate, at some point during the rotation the space is no longer in communication with the inlet port and the flow of refrigerant to the space is cut off. After the inlet port is closed, the refrigerant is compressed as the rotors continue to rotate. At some point during the rotation, each space intersects the associated outlet port and the closed compression process terminates. The inlet port and the outlet port may each be radial, axial, or a hybrid combination of an axial port and a radial port. The compression pocket opening and closing (particularly discharge port opening) are associated with pressure pulsations and resulting sound. Sound suppression has thus been an important consideration in compressor design. Many forms of compressor mufflers have been proposed.
Additionally, various transient conditions may tend to cause reverse flow through the compressor. For example, upon a power failure or other uncontrolled shutdown high pressure refrigerant will be left in the discharge plenum and downstream thereof in the refrigerant flowpath (e.g., in the muffler, oil separator, condenser, and the like). Such high pressure refrigerant will tend to flow backward through the rotors, reversing their direction of rotation. If rotation speed in the reverse direction is substantial, undesirable sound is generated. For some screw compressors, damage to mechanical components or internal housing surfaces can also occur. Accordingly, a one-way valve (a check valve) may be positioned along the flowpath to prevent the reverse flow. Other forms of compressor (e.g., scroll and reciprocating compressors) may include similar check valves.